Metal complexes of C-functionalized macrocyclic dioxotetraamines bearing 8-hydroxyquinoline: Stability in aqueous solutions

Two novel 3-hydroxyquinoline connected dioxotetraamines have been designed and synthesized, and have been characterized by elemental analysis, IR, mas s spectra and H-1 NMR. The two ligands L-1 and L-2 have two chelating group s. Each can react with a transition metal ion forming complexes. Potentiome tric titrations have been performed in 0.1 mol/L NaNO3 at 25 degreesC givin g the 1:1 stability constants. Coupled with UV spectroscopy the affinity of 8-hydroxyquinoline and dioxotetraamines to transition metal ions were comp ared and the possible structure of the metal complex species in solution wa s discussed. The results show that as to Mn2+, Zn2+ and Co2+, 8-hydroxyquin oline is a stronger chelating reagent than dioxo[13] or [14]tetraamine macr ocycles and at 1:1 molar ratio (M:L), the former binds in 100% to the metal ions, while the dioxotetraamines can be only partially or not coordinated.